What Is Evolution?

    Evolution is a scientific theory often attacked by religious groups because it contradicts their belief that all animals and humans were created separately by God, and that humans are a special creation of God that are the prime focus of His creation. He created man to have a special relationship with them, and He values humans more than any other creation and has given humans rule over the earth. Because of religious beliefs there are lots of misunderstandings about evolution, both intentional and unintentional, and in this blog post I would like to make what evolution is easily understood for the layperson.

    

    So what is evolution? Simply put, evolution is the scientific theory that all living organisms (which are all organisms that share the self-replicating system of DNA) descended from a common ancestor. The original or universal common ancestor began reproducing through the self-replicating system of DNA, and over millions of years it has filled the earth with its wide variety of different offspring. This offspring includes things as different as humans, dogs, crocodiles, bananas, peas, etc. Yes, we share a common ancestor with bananas and peas, which have the same self-replicating system of DNA we have.

    How has a universal common ancestor led to such a wide variety of different living organisms? The original or universal common ancestor has led to such a wide variety of living organisms through an accumulation of genetic variations over millions of years. Genetic variation is simply changes in things such as bone mass, height, size, intelligence, strength, speed, etc. Generic variations happen when there are slight differences in the genetic codes of one organism compared to another one, or there is a mutation in a gene during reproduction. It is an accumulation of these genetic variations over many many many generations or over the course of millions of years that lead to the wide diversity of living organisms we have on our planet.

 

    What are ways genetic variations accumulate? So genetic variations are slight differences or mutations in the genetic code of one organism compared to another, and result in differences such as size, strength, speed, intelligence, etc., between individuals, but how do these genetic differences continue to accumulate through many generations and lead to a new species forming? There are four main ways evolution creates genetic variations that are then accumulated: natural selection, mutation, genetic drift, and gene flow. 

    Natural selection - Traits or features that allow an organism to survive longer than its peers and/or to reproduce more offspring than its peers continue getting passed on through many generations of offspring until it dominates the population of that organism. Many traits or features can be beneficial for passing on genes and over many many generations these traits or features can accumulate and form an entirely new species.

    Mutation - Errors can occur when an organism's genetic code is being copied during reproduction, and on rare occasions this can result in new beneficial features or traits that give an organism a survival advantage when then leads to natural selection taking its course.

    Genetic Drift - Certain traits or features come to dominate a population (typically a small population) sheerly by chance events, which could be due to natural disasters, things such as hungers, etc. (https://www.khanacademy.org/science/ap-biology/natural-selection/population-genetics/a/genetic-drift-founder-bottleneck). If the traits or features that come to dominate a population through chance events prove beneficial, this could lead to an accumulation of genetic variations as the population increases and natural selection takes over.

    Gene Flow - When one population of a species migrates from one area to another and begins interbreeding with another population of the same species genetic variations are created. A practical example of gene flow would be if when European settlers arrived in the Americas they began interbreeding with the Native Americans. The Native Americans are now having the genetics of European settlers introduced into their gene pool and new possibilities for genetic variations are created, for example it may now be possible for there to be blonde hair and blue eyes in the Native American population where there wasn't a gene for that trait being passed through the population previously. (https://www.britannica.com/science/gene-flow)

    How do we know evolution is a fact? Evolution is bedrock scientific theory (theory meaning it has been observed and tested repeatedly and confirmed more strongly every time), and due to the nature of the evidence supporting evolution it would be nearly impossible for the entire theory to be overturned. Four lines of evidence that could have easily been the death knell for the theory of common ancestry but have instead strengthened the theory are homology, genetic evidence, the fossil record, and geographical distribution. (https://www.khanacademy.org/science/biology/her/evolution-and-natural-selection/a/lines-of-evidence-for-evolution)

    Homology - If certain species have evolved from a common ancestor one would expect to find similar features or bone structures that are clearly the same but have been adapted and changed for different purposes. This is clearly seen in that humans, whales, bats, and dogs all have the same forelimb that has been adapted and changed for different purposes, such as walking (dogs), swimming (whales), holding things (humans) and flying (bats). The forelimb of all of these species has the same bone structure and five digits at the end of the forelimb, despite how widely different these forelimbs are used. 

    Genetic Evidence - First, all living organisms share the same self-replicating system of DNA, something that would be necessary in order for common ancestry to be viable and so would be expected under the theory of evolution. This one simple piece of evidence could have completely eradicated the idea of common ancestry among all living organisms once and for all if every species or most species had a unique form of self-replicating genetics that were incompatible with the self-replicating genetics of other organisms.

    Second, the more recently organisms have split from a common ancestor the more similar genes in their gene pool will be, and the more distantly organisms have split from a common ancestor the more differences there will be in the genes of each organism's gene pool, due to there being more time for mutations and genetic variations to occur in each organism's gene pool. How closely related organisms are can be traced through the similarities and differences in the genes of two organisms' gene pools. If two species inherited the same gene from a common ancestor, for example, the more similar that gene is in each species' DNA the more closely those species are related. Genetics can then reflect and more strongly affirm the evolutionary paths one would expect to see among different living organisms if they evolved from a common ancestor. 

    The Fossil Record - Organisms die and become fossilized in rocks, and over time those rocks become covered with other rocks above them that later animals are then fossilized in, and this continues on for millions and millions of years and creates the geological layers we have today. The order and change of species from the oldest rocks on the bottom to the newest rocks on the higher layers reflects the evolutionary path of common ancestry one would expect to see if evolution were true. One can see the path of organisms evolving into other organisms over time through the different layers of rocks. This could easily have dismissed evolutionary theory as well had the rocks had no special order of fossils from the oldest to the newest, and all living organisms (including some that are alive today) are spread out haphazardly together among all the layers.

    Geographical Distribution - If common ancestry were true one would expect to see unique species on isolated islands or continents because their ancestral species became isolated on that island or continent and evolved uniquely to survive in that specific environment. For example, with common ancestry one would only expect to see Marsupials in Australia and nowhere else in the world because the common ancestor of Marsupials became isolated on that continent by water and led to the all the Marsupials that live in Australia today.  One would not expect to see Marsupials all over the world because their common ancestral species was isolated to Australia and the common ancestor of Marsupials evolved uniquely in response to that environment it was isolated to.

I hope this helps those who read it better understand evolution and why it is a scientific fact. Understanding evolution is important because it helps give us an objective way to look at the relationship of our species to all other species and to have an accurate view of the reality in which our species lives. We cannot have a fully formed and healthy worldview without being fully informed of how the reality within which we live works.